Add ability to drag and drop images into the description section when creating
new Kanban cards. Images are saved to a temp directory and their paths are stored
with the feature for agent context.
- Create DescriptionImageDropZone component with drag/drop support
- Integrate with Add Feature dialog in board-view
- Add FeatureImagePath interface to track temp file paths
- Update saveFeatures to persist imagePaths
- Add saveImageToTemp to mock electron API
- Add test utilities for image upload testing
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
